I've thought about this before... Wikipedia covers unstructured data, but we need something to be its analog for structured data. Others have pointed out freebase (which kicks ass IMO), but there's also swivel (http://www.swivel.com/). Swivel's correctness model, however, doesn't seem to be the same open idea that freebase is. It seems more to be focused on data "authorities" and "official" data providers as opposed to just an "accuracy of the masses" system that the more open sites rely on.